The present invention is directed to a process for the preparation of chlorinated alkylanilines, in particular chlorinated 2,6-dialkylanilines.
Meta-chlorinated 2,6-dialkylanilines are important starting materials for the preparation of chlorinated 4,4′-methylene-bis(2,6-dialkylanilines) which are used as chain extenders or cross linking agents in the polymer industry, for example in the preparation of polyurethanes and epoxy resins.
Beard and Hickinbottom (J. Chem. Soc., 1958, 2982-2986) describe meta-selective chlorination of 2,6-dialkylanilines starting from the corresponding N-chloro-acetanilides. This reaction, however, suffers from the disadvantage of additional protection and deprotection steps in order to obtain the free amine.
U.S. Pat. No. 3,962,336 discloses the preparation of 5-chloro-2-toluidine by reacting 2-toluidine hydrochloride with chlorine. Direct chlorination of other anilines, however, leads to the formation of product mixtures as described in GB-A-1 521 136.
U.S. Pat. No. 4,401,833 discloses the direct chlorination of the hydrochlorides of 2,6-dialkylanilines in an organic solvent system, wherein the hydrochlorides are sparingly soluble. Consequently, the bulk of the hydrochloride is present in crystalline form as a suspension. This process, however, results in 4-chloro-2,6-dialkylanilines only.
The object of the present invention, therefore, is to provide an effective and cost efficient process for the meta-selective chlorination of alkylanilines, in particular 2,6-dialkylanilines.